Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-11-21
2004-03-16
Truong, Duc (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S137000, C528S162000, C528S163000
Reexamination Certificate
active
06706845
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to low free formaldehyde and low formaldehyde emission phenol formaldehyde resins. In particular, this invention relates to phenol formaldehyde resins that have low free formaldehyde when produced, that maintain their low free formaldehyde levels during storage, and that demonstrate low levels of formaldehyde emissions during processing, curing, and thereafter.
BACKGROUND OF THE INVENTION
Phenol aldehyde resins have many commercially important uses. Resins having various mole ratios of aldehyde to phenol are known in the industry, and are selected to provide desired characteristics, depending upon the intended use of the resin.
Resole resins, i.e., those resins formed by the condensation of a phenol with an aldehyde in the presence of alkaline catalyst, are an important class of phenol aldehyde resins. Because resole resins are hardened by heat, they often are used as a binder which is applied to a substrate, then hardened by application of heat, often under pressure.
Phenol formaldehyde resole resins are a particularly important class of phenol aldehyde resole resins. Phenol formaldehyde resole resins often are used as binders, e.g., for manufactured boards, chipboard products, fibrous products, or laminated products. Resins for laminated products must exhibit properties and characteristics, such as good substrate penetration, and produce laminates with good dimensional stability, good postformability, low panel warpage, low water absorption and high thermal blister resistance, that other resins need not exhibit. However, such known resins have formaldehyde levels which cause formaldehyde to be released into the environment during processing, storage of the treated substrate, and cure. Such formaldehyde release is undesirable, particularly in an enclosed place. Formaldehyde may be inhaled by workers and may come in contact with the eyes, the mouth, and other parts of the body. Formaldehyde is malodorous, and is thought to contribute to human and animal illnesses. Therefore, it is desirable to reduce the level of free formaldehyde in resins and the release of formaldehyde during processing of such resins into the environment.
Formaldehyde is not the only component that may be undesirably released into the atmosphere from a phenol-formaldehyde resin. For example, phenol also may be released into the environment. Thus, any measures taken to reduce free formaldehyde in the neat resin and formaldehyde emissions during processing, cure, and use desirably do not increase, and preferably decrease, phenol emissions. Traditionally, reductions in free phenol levels have been most easily achieved by increasing the formaldehyde to phenol molar ratio. However, this usually tends to increase the level of free formaldehyde in the resin and thus increase the amount of formaldehyde released during processing and cure. A process that can significantly reduce the free formaldehyde in a resin and the formaldehyde emissions during processing can therefore allow the use of higher molar ratio resins to, in turn, reduce free phenol levels and phenol emissions during processing.
Various techniques have been used to reduce free formaldehyde in and formaldehyde emissions from formaldehyde-based resins. In particular, various formaldehyde scavengers (i.e., chemicals usually added to the resin during or after its preparation) have been used in an attempt to reduce formaldehyde emissions. Use of a formaldehyde scavenger, particularly at high levels, often is undesirable, however, not only because of the additional cost, but also because it can adversely affect the characteristics or properties of the cured resin and therefore the finished product made with the resin.
It is also well known that formaldehyde emissions can, in part, be controlled by the addition of free urea to an uncured resin system. Urea often is selected because it is inexpensive compared with other formaldehyde scavengers. Urea acts as a formaldehyde scavenger both during, and subsequent to, the manufacture of the resin. It can be added by the resin manufacturer or prior to use by the end user to scavenge residual free formaldehyde. Urea typically is added directly to phenol formaldehyde resin to produce a urea-extended phenol formaldehyde resole resin. The resin can be further treated or applied as a coating or binder, as desired, and then cured. These resins typically are used in, for example, the insulation industry as part of an adhesive for glass fibers. In an insulation application, the urea addition also contributes to improved anti-punk characteristics for the cured binder. However, in laminating applications, urea in quantity sufficient to yield very low free formaldehyde and formaldehyde emissions degrades laminate performance, as water resistance is decreased and laminate high-temperature blister time performance is reduced. Similarly, use of ammonia in such quantities has a deleterious effect on storage stability.
Other formaldehyde scavengers commonly used include dicyandiamide and melamine. However, these scavengers are expensive and add significantly to the cost of the resin. They also can have solubility/compatability problems in the phenol-formaldehyde resin at high levels of scavenger addition.
Even when a combination of formaldehyde scavengers is utilized at the end of the resin A-stage manufacturing process in an attempt to reduce free formaldehyde and ameliorate formaldehyde emissions during B- and C-stage processing while minimizing the adverse effects on the resin, these scavengers leave much to be desired when added to a completed A-stage resin. Typically, the free formaldehyde in the resin can be low initially, i.e., less than 0.10%, but it can increase significantly over 24 to 48 hours. Typically, resins utilizing scavengers in this manner exhibit free formaldehyde levels that can increase into the 0.25-1.0% range over several days.
Another technique for lowering formaldehyde emission levels is to use relatively high catalyst levels. While higher catalyst levels reduce free formaldehyde levels, they do not, by themselves, reduce the total free formaldehyde to less than 0.10%.
Thus, there exists a need for a phenol formaldehyde resole laminating resin exhibiting low free formaldehyde in the resin and low formaldehyde emissions not only during processing but also during storage of treated substrate prior to the final processing (laminating) step. There also exists a need for a method for making such low formaldehyde emission resins.
SUMMARY OF THE INVENTION
The invention is directed to phenol formaldehyde resole laminating resin that exhibits low free formaldehyde immediately after manufacture; low formaldehyde emissions during the substrate treating process; and low formaldehyde emissions of the substrate during storage prior to final pressing and curing of the laminate. The invention also is directed to a method for making such a low formaldehyde emission resin.
DETAILED DESCRIPTION OF THE INVENTION
The invention is directed to a phenol formaldehyde resole laminating resin that exhibits low free formaldehyde during manufacture and cure, and low formaldehyde emissions during the substrate treating process and storage prior to final pressing and curing of the laminate. The invention also relates to a method for manufacturing the resin of the invention.
The inventors have discovered that use of a relatively large quantity of catalyst, as compared with the quantity used for typical laminating resins, in combination with the addition of one or more formaldehyde scavengers during later portions of the A-stage of the resin cook, yields a phenol formaldehyde resole resin having low free formaldehyde and low formaldehyde emissions during B- and C-stage resin processing and curing. Such resin is particularly adapted for use in manufacture of paper-based laminate products.
In accordance with the method of the invention, an A-stage phenol formaldehyde resin is prepared under alkaline conditions and in the presence of relatively large quantity of catalyst. After an initial cook,
Ingram W. Hayes
Letchas Mary
McVay Ted M.
Banner & Witcoff , Ltd.
Georgia-Pacific Resins Inc.
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